1. Field of the Invention
The present invention relates to a hovering-type head slider carrying a magnetic head for performing recording and reproduction on and from, for example, a magnetic disc or a magneto-optical disc, and to a magnetic disc device.
2. Description of the Related Art
FIG. 22 shows an example of the construction of a conventional hard disc drive device which is incorporated in or connected to a computer or the like.
In FIG. 22, a hard disc drive device 1 includes a casing 2 that is formed of an aluminum alloy or the like. A spindle motor (not shown) is arranged in a flat section of the casing 2. Further, there is provided a double-sided magnetic disc 3 which is rotated at a fixed angular velocity by this spindle motor.
Further, an arm 4 is mounted to the casing 2 so as to be swingable around a vertical axle 4a. A voice coil 5 is attached to one end of this arm 4, and a head slider 6 is attached to the other end thereof.
Magnets 7a and 7b are attached to the casing 2 such that the voice coil 5 is positioned between these magnets. The voice coil 5 and the magnets 7a and 7b constitute a voice coil motor 7.
When an electric current is supplied from outside to the voice coil 5, the arm 4 is rotated around the vertical axle 4a due to the force generated by the magnetic fields of the magnets 7a and 7b and the electric current flowing through the voice coil 5, whereby the head slider 6, which is attached to the other end of the arm 4, is moved substantially radially with respect to the magnetic disc 3, as indicated by arrows X in FIG. 23. As a result, a magnetic head 8 (See FIG. 24), which is provided on the head slider 6, performs a seek operation on the magnetic disc 3. In this way, information is recorded or reproduced on or from a predetermined track of the magnetic disc 3.
The head slider 6 is constructed as shown in FIG. 24. In FIG. 24, the bottom surface of the head slider, that is, that surface of the head slider which is to be opposed to the magnetic disc 3, is directed upwards. Rails 6a and 6b serving as air bearing surfaces are formed on either side portion of the lower surface of the head slider 6, which surface is one of the main surfaces of the head slider. Further, tapered portions 6c and 6d are provided at the air flow inlet ends of the rails 6a and 6b, whereby, when the head slider 6 is brought close to the surface of the magnetic disc 3 rotating in the direction of the arrow Y, as shown in FIG. 23, the head slider 6 receives a lift due to the air flow introduced into the gap between the rails 6a, 6b of the head slider 6 and the surface of the magnetic disc 3.
Due to this lift, the head slider 6 and the magnetic head 8, which is attached to this head slider 6, hover over the surface of the magnetic disc 3, keeping a minute distance (hovering distance) d from the surface of the magnetic disc 3, as shown in FIG. 25. Thus, damage due to wear of the magnetic disc 3, which would occur if the magnetic head 8 were in direct contact with the surface of the magnetic disc 3, can be prevented. Generally speaking, this hovering distance d is approximately 0.1 .mu.m and, at the research level, approximately 0.05 .mu.m.
In this hovering-type head slider 6, constructed as described above, even when the surface of the magnetic disc 3 has some surface irregularities, as shown in FIG. 25, the hovering distance d of the head slider 6 and the magnetic head 8 with respect to the same track as measured from the surface of the magnetic disc 3 can be kept substantially constant.
The hovering-type head slider 6, constructed as described above, however, has a problem in that the hovering distance of the hovering-type head slider 6 fluctuates, in other words, a so-called dynamic variation in the hovering distance occurs when an impact is applied to the magnetic disc 3 or when the hovering-type head slider 6 cannot sufficiently respond to surface irregularities, undulations, etc. of the magnetic disc 3.
Further, when the magnetic disc 3 is rotated at a fixed angular velocity, the linear velocity in the outer periphery of the disc is higher than the linear velocity in the inner periphery thereof. As a result, there is a relatively great amount of disparity in the hovering distance d of the slider 6 between the outer and inner peripheries of the magnetic disc 3. That is, the linear velocity in the outer periphery of the magnetic disc 3 is higher than the linear velocity in the inner periphery thereof, and the resultant hovering distances correspond to these linear velocities. As a result, a so-called static variation in hovering distance is generated.
When the arm 4 rotates around the vertical axle 4a, the head slider 6 makes not a linear but an arcuate movement with respect to the radial direction over the surface of the magnetic disc 3, as shown in FIG. 26. Thus, as shown in FIG. 27, the center line 6e of the head slider 6 is deviated from the tangential direction 3a of the track of the magnetic disc 3, and a so-called skew angle .theta.s is generated. This skew angle .theta.s varies in accordance with the distance from the center of the magnetic disc 3.
That is, when the skew angle .theta.s increases, the efficiency in the conversion to the lift of the dynamic pressure between the surface of the magnetic disc 3 and the slider 6 is reduced, with the result that the hovering distance d is reduced.
Thus, the hovering distance d, which is larger in the outer periphery, decreases due to the skew angle .theta.s. Here, the variation in the hovering distance d due to the linear velocity is linear, whereas the reduction in the hovering distance d due to the skew angle .theta.s is quadratic and not linear. Thus, as long as the conventional slider 6 shown in FIG. 24 is used, it is difficult to have the requisite balance between the linear velocity and the skew angle .theta.s over the entire radial range of the magnetic disc 3.
Thus, due to the mutual action of the above-mentioned static variation in hovering distance and the reduction in hovering distance attributable to the skew angle, the S/N at the time of recording/reproduction cannot be kept constant, so that it is impossible to perform accurate recording and reproduction on and from a desired track by means of the magnetic head 8.
In view of this, there has been proposed, for example, a head slider 9, which is, as shown in FIG. 28, equipped with hand-drum-shaped rails 6e and 6f that are formed so as to diverge toward both ends from a position near the center with respect to the direction of the air flow.
By using this head slider 9, constructed as described above, the entire length of each of the rails 6e and 6f contributes to the hovering of the head slider 9 with respect to an air flow having a skew angle .theta.s. Thus, the reduction in the hovering distance when the skew angle .theta.s is large is mitigated, with the result being that a hovering-distance characteristic which is relatively stable on the whole with respect to the variation in the skew angle can be obtained.
However, in the above head slider 9, which is equipped with the hand-drum-shaped rails 6e and 6f, it is impossible to completely eliminate the variation in the hovering distance when the skew angle .theta.s is zero since the lift then generated by the air flow is excessively large.
Thus, as described above, the distance between (the head slider 9 and the magnetic head 8) and the magnetic disc 3, that is, the spacing, fluctuates even in the case of a slight variation in the hovering distance since nowadays the hovering distance is as small as approximately 0.1 .mu.m, with the result being that the spacing loss is not constant. Thus, it is impossible to utilize the performance of the magnetic disc to the utmost. Further, in extreme cases, the magnetic head comes into contact with the surface of the magnetic disc 3, thereby damaging the recorded data.